Polymer materials typified by, for example, polyolefin resin-, polyester resin-, polyamide resin-, polyacrylate resin-, polycarbonate resin-, and polyimide resin-based materials have been widely utilized as various industrial materials. Those general-purpose polymer materials are each excellent in mechanical physical properties such as heat resistance and impact resistance, but each hardly decompose under a natural environment, so each of the materials remains in the ground semipermanently when buried in the ground.
Meanwhile, biodegradable materials have been attracting attention in recent years, and the development of biodegradable resins such as an aliphatic polyester resin has been actively performed. Plant-derived resins have been attracting attention because of their potential to serve as carbon-neutral materials since carbon dioxide produced by the decomposition of the resins may be such that carbon dioxide originally present in the air is fixed.
Of the plant-derived resins, polylactic acid has been mainly applied to, for example, packages for OA systems and home appliances, automobile parts, bottles, films, sheets, and eating utensils. In general, however, heat resistance is often needed in those applications. The polylactic acid, which is an aliphatic polyester resin, has a glass transition temperature (Tg) of about 57 to 60° C., and does not have sufficient heat resistance. Therefore, at present, it is difficult to use the polylactic acid, which has low heat resistance, so the polylactic acid has been actually finding use in limited applications. There has been a growing demand from the industrial world for a plant-derived resin with improved heat resistance because the resin can be expected to find use in a variety of applications. Accordingly, various kinds of contrivance have been made for improving the heat resistance of a plant-derived resin.
To be specific, a polyester resin using a plant-derived material has been reported as one approach to improving the heat resistance of a plant-derived resin (Japanese Patent Application Laid-Open No. 2007-146153).